Remove any tendons from the chicken and cut it into approximately 4 to 5 centimeter cubes. In a deep bowl, whisk together the egg, kefir, flour, cornstarch, and chili powder until smooth and creamy, then season generously with salt and pepper.

Add the chicken pieces to the egg and flour mixture and stir well so that each piece is completely coated with the egg mixture; let marinate for approximately 5 to 10 minutes.

Place the panko breadcrumbs in a bowl or deep plate and season generously with salt and pepper. Preheat the air fryer to 230°C (450°F) and, in the meantime, coat the chicken pieces in the panko breadcrumbs until completely covered, then place them on a plate or board.

Grease the air fryer basket with a little cooking spray or oil and place the chicken fillets side by side in the basket.

Cook chicken pieces in an air fryer at 230°C for 7 minutes, depending on their size, until they are nicely crispy on the outside and the internal temperature reaches 74°C. Repeat the process until all the chicken pieces are cooked.

Meanwhile, for the sauce, mix together mayonnaise, sriracha and sweet chili sauce.

To serve, spread the sauce over the crispy baked chicken pieces and/or serve it as a dip with the Bang Bang Chicken.